An electrical cutout is a device used to protect an electrical power distribution grid. If there is a surge in the electrical current on the line, for example, a fuse on the cutout is blown, thereby cutting off power to a section of the grid. As a result, a section of the grid loses power. Though a section of the grid experiences power loss, the entire grid is protected from the surge and remains operational.
Electrical cutouts contain three parts: a fuse, an insulator, and a fuse link. When a fuse is blown, physical force is exerted on the insulator. Consequently, the insulator must be manufactured with sufficient strength to withstand damage from the fuse when it is blown. Consequently, insulators have been made with porcelain or some other ceramic material for added strength to prevent damage when the fuse element activates. For example, U.S. Pat. No. 4,774,488 to Field, the disclosure of which Applicants hereby incorporate by reference in its entirety, teaches the use of a porcelain insulator.
The ceramic insulators, however, are heavy and bulky; they require specialized assembly fixtures or processes and are awkward and difficult to handle and ship. The ceramic insulators are also brittle and easily chipped or broken.
Problems have arisen with electrical cutouts. One such problem occurs when electricity flashes directly from a conducting surface to a grounded surface while the fuse assembly is in the open or closed position. This phenomenon is referred to as “flashover.” The electricity travel gap between the conducting surface and the grounded surface is called the “strike distance.”
Another problem with conventional cutouts occurs when the electrical current travels or “creeps” along the surface of the insulator, bypassing the fuse assembly. “Creep” results when the insulator has an inadequate surface distance. This may occur when water, dirt, debris, salts, air-borne material, and air pollution is trapped at the insulator surface and provide an easier path for the electrical current. This surface distance may also be referred to as the “leakage,” “tracking,” or “creep” distance of a cutout.
Because of these problems, cutouts must be made of many different-sized insulators. Cutouts are made with numerous insulator sizes that provide different strike and creep distances, as determined by operating voltages and environmental conditions. The strike distance in air is known, thus insulators must be made of various sizes in order to increase this distance and match the appropriate size insulator to a particular voltage. Creep distance must also be increased as voltage across the conductor increases so that flashover can be prevented.
Cutouts with plastic or polymeric insulators have been designed; however, such insulators are of complicated design and labor-intensive manufacture. Examples of such cutouts include U.S. Pat. No. 5,300,912 to Tillery et al., entitled “Electrical Cutout for High Voltage Power Lines,” the disclosure of which is incorporated herein by reference. However, Tillery et al. utilizes an injection-molded insulator with a complicated non-solid cross-sectional configuration (Col. 6, 11. 20-22) with skirts mounted thereon (Col. 4, 11. 53-54).
Other insulators used in cutouts use “fins” or “sheds” which require additional time and labor for assembly. For example, U.S. Pat. No. 5,128,648 to Brandi, entitled “Line Cutout for Electrical Distribution System,” the disclosure of which is hereby incorporated by reference, discloses the use of a plurality of circular “fins” (Col. 3, 11. 45-47) that are placed around a rod (FIG. 3). In U.S. Pat. No. 4,870,387 to Harmon, entitled “Beam Strengthened Cutout Insulator,” the disclosure of which is incorporated herein by reference, an insulator formed of glass bead and dehydrated alumina-filled bisphenol is disclosed (see Col. 4, 11. 34-36) which utilizes “skirts” having an oval-shaped cross-sectional configuration (Col. 4, 11. 44-48).
Therefore, there exists a need for simple design that facilitates ease in the manufacture of the many different-sized cutouts and insulators the electrical power industry requires. There also exists a need for a lighter insulator that allows for greater ease in handling and shipping. Further, there exists a need for an insulator, which will not trap water, dirt, debris, salts, and air-borne material and thereby reduce the effective creep distance. Finally, there exists a need for a stronger insulator, which will not chip or break when a fuse is blown and which can withstand the tension forces exerted by electric power lines.
The present invention is directed to overcoming these and other disadvantages inherent in prior-art systems.